1. Field of the Invention
The present invention relates to a star configuration network system and, more particularly, to a star configuration network system characterized by a novel method for designating the addresses of nodes constituting a network, by new procedures for establishing a line and by an improved method for transmitting data over the line.
2. Description of the Related Art
There exist so-called local area networks (LAN's) that connect workstations or personal computers located in a limited area. All nodes constituting such a network are each assigned an address when the network system is set up.
One known procedure for establishing a line in a network system is the LAPD (link access protocol D-channel) of the ISDN (integrated services digital network). The frame structure of the LAPD conforms to the frame format of the HDLC (high-level data link control). In this frame structure, a flag comes first that identifies the frame, followed by an address part that identifies a logical link, and lastly by a control part.
Known small-scale network systems include the HBS (home bus system), D2B (domestic digital bus system) and LANC (local application control bus system). In the HBS and D2B, data is transmitted after inquiries are made between the terminals involved (called the inquiry system hereunder). In the LANC, data is continuously transmitted while the line is being established (called the constant flow system hereunder). In connection with the present invention, European Patent Application Pub. No. 0,467,305 discloses a multi-master system wherein a computer is connected in daisy chain with audio-visual appliances for repeating packet signals and predetermined control signals therebetween under integrated control.
In systems such as a computer network where few nodes are relocated once each given an address, the conventional method of assigning addresses to the individual nodes is effective from a control point of view. However, the effectiveness of the method is diminished in systems such as an audio-visual network system configuring AV appliances because the nodes of such a system need to be addressed every time any of the nodes is removed or relocated, which occurs often.
The LAPD controls are intended for use with public switched networks. Thus the control procedures of the LAPD are complex and can overburden the control scheme of small-scale networks such as audio-visual appliance networks. In addition, the LAPD is not suited for networks whose nodes are not each assigned an absolute address.
The inquiry system adopted for the HBS and D2B is capable of acquiring information from a large number of terminals, but is not suitable for obtaining specific information from an individual terminal on a real time basis. For example, suppose that a video tape recorder (VTR) under the inquiry scheme is inquired as to its counter information repeatedly and responds thereto. In that case, one disadvantage is that the responses may fail to keep up with the repeated inquiries. Another disadvantage is that while the VTR is responding to an inquiry, it is impossible to acquire information from the other appliances configured. The constant flow system adopted for the LANC allows, say, counter information to be obtained in real time but requires huge amounts of information to be handled if a large number of appliances are configured and need to be tapped for information.